Optimal Design of Groundwater-Quality Sampling Networks with Three-Dimensional Selection of Sampling Locations Using an Ensemble Smoother

Abstract

In groundwater-quality monitoring it is important to consider that groundwater-contaminant concentration can vary vertically. To find the actual concentration of contaminants in a groundwater plume, it may be necessary to sample at different depths at the same location. This can be expensive due to the initial cost of the wells and the costs of multiple chemical analyses for each round of sampling. A sampling optimal design in three dimensions (3D) allows identifying the contaminant-concentration variations in all spatial directions at a minimum cost. The objective of this paper is to extend a methodology for the optimal design of groundwater-quality sampling networks previously introduced by the first author of this paper, to include the selection of measurements at different depths. The method is based on the application of a version of the ensemble smoother, a stochastic transport model, and a sequential optimization method. The method is demonstrated for the design of 3D groundwater-monitoring networks in two hypothetical problems.